1. Field of the Invention
The present invention relates to a bottle made of a saturated polyester resin, and more particularly to a neck orienting method of orienting not only the trunk but also the neck of the bottle thereby to enhance the physical properties and durability of the bottle neck.
2. Description of the Prior Art
Saturated polyester resins such as polyethylene terephthalate have recently been used in various fields because of their excellent physical properties and durability. However, these excellent properties are not exhibited until the moldings of such resins are subjected to an orienting treatment.
Therefore, the molding method of the saturated polyester resin bottles is generally limited to the blow molding method.
The current molding procedures of the saturated polyester resin bottles include the steps of injection-molding a bottomed cylindrical parison as a primary molding, orienting the neck of the parison, while being held in a blow mold, in the axial direction with the use of an orienting pin, and injecting a fluid under pressure into the oriented parison to blow-mold a bottle having a shape according to a blow mold. As is apparent from those molding procedures, however, the neck of the bottle is completely left unoriented.
As a result, the neck of the bottle exhibits inferior physical properties and durability compared to other portions. For instance, if the bottle thus molded is filled with alcohol of high concentration, only its neck (which has not been biaxially oriented) is whitened and becomes mechanically fragile due to attack of the alcohol.